Expansion of a light gas working fluid, e.g. hydrogen or helium, at high temperature and pressure can accelerate projectiles to great velocity because of the fluid's very high sound speed, which is proportional (in simplest form) to the square root of temperature over molecular or atomic weight.
Prior work with light gas launch has largely focused on development of hardware appropriate to this objectives. For example, in U.S. Pat. No. 8,979,033 (2015) and U.S. patent application Ser. No. 14/659,572 (2015), Hunter et al. disclose sea and land-based light gas launcher variants or space launch applications. In U.S. patent application Ser. No. 14/642,720 (2015), Cartland describes the conditioning of the requisite large mass of light gas to high temperature and pressure using a heat exchanger, i.e. without relying on adiabatic compression. In U.S. Pat. Nos. 8,536,502 (2013) and 8,664,576 (2014), Hunter et al. disclose spinning and non-spinning space launch vehicles designed for hypersonic impulsive launch, atmospheric egress, and orbital insertion.
In contrast to the prior hardware oriented work discussed above, the emphasis here is on methods, specifically the efficient orbital mechanics or astrodynamics of orbital launch and rendezvouz, as well as beyond Low Earth Orbit (LEO) missions. Although developed for light gas launchers, the methods disclosed apply more generally to many impulsive space launch concepts, including electromagnetic launchers, powder guns and more exotic technologies.
A light gas launcher might at first appear somewhat constrained by its size (and hence orientation) to a limited range of applications, but this is not true. A mobile sea-based launcher can be moved to just about any launch latitude, and combined with flexibility in azimuth, can access the full range of orbital inclinations efficiently. In addition, both launch elevation and muzzle velocity can be adjusted to service any orbital altitude efficiently. So a sea-based launcher is extremely agile in its ability to address a wide range of missions, no more kinematically constrained than a conventional rocket.
A land-based launcher is somewhat less agile, being limited by launch site latitude and launcher orientation to fixed inclination (or a narrow range of inclination), though still commanding some flexibility in altitude. Even so, this isn't necessarily a shortcoming for certain applications if the launcher is properly matched to the mission, as will be discussed later.